Ceramic metal halide lamps contain fillings which comprise besides a starter gas also metal halide salt mixtures such as NaCe iodide, NaTl iodide, NaSc iodide, NaTlDy iodide, or combinations of these salts. These metal halide salt mixtures are applied to obtain, inter alia, a high luminous efficacy, a specific color-corrected temperature, and a specific color rendering index.
Generally, such ceramic metal halide lamps comprise a discharge vessel enclosing a discharge space comprising the filling of the metal halide salt mixtures. The discharge space further comprises electrodes between which a discharge is maintained. Typically, the electrodes pierce through the discharge vessel. To fill the ceramic metal halide lamp with the metal halide salt mixture, a filling-opening is typically provided which is subsequently closed with a closing-plug.
An embodiment of such a ceramic metal halide lamp is known from the Japanese patent application JP 10284002. In the known discharge lamp, the lamp consists of an airtight container having a plug made of a material having almost the same coefficient of thermal expansion for aligning a pair of electrodes. The container further comprises an exhaust opening. The discharge medium is introduced into the container through the exhaust opening, which is then closed by means of a T-shaped plug that fits the opening in the container. The T-shaped plug is fused to the wall of the container through irradiation with a laser that is aimed at the T-shaped plug. A disadvantage of the known ceramic metal halide lamp is that, when the container is miniaturized, the T-shaped plug cannot be closed without increasing the temperature of the entire burner, heating up the filling.